As others have noted, the F5 has a decided heft to it; while I personally don't find its size problematic (I often carry it around with a 80-200 F2.8D ED attached), others might. The F6, without the optional MB40, is decidedly lighter; I purchased the drive unit shortly after picking up the camera, because I felt it gave the camera better balance and handling with longer lenses. While it added a bit of weight, the package still feels somewhat lighter than the F5 ( I have the two in front of me as I write, but alas, no scale to weigh each). In either case, two cameras with exceptional ergonomics!